This invention relates to an expansion joint which employs bellows which are externally pressurized, which is pressure-balanced, and which is located in an angled-flowpath.
Several needs have persisted in dealing with the expansion and contractions of conduits or pipelines through which hot or cold fluids are flowed, e.g. steam and chemical process liquids and gases. Simple bellows type joints have been made which are inserted in the conduit and provided thermal contraction and expansion leeway for the conduit by correspondingly expanding or contracting. These have proven most unsatisfactory, particularly in lines through which high pressure fluids are flowed. In these designs, the pressure is applied internally to the bellows and tends to expand the bellows outwardly. It is known that a bellows can withstand more pressure exerted externally upon it than it can withstand when the pressure is exerted internally. Hence, the pressure ratings of an internally pressurized bellows is less than that of an externally pressurized bellows. Also when a crack develops in an internally pressurized bellows catastrophic failure often occurs as the crack quickly erupts into a gaping hole resulting in large and possibly dangerous releases of the fluid within the expansion joint. For this reason, shields are often placed over the expansion joints, or externally pressured bellows expansion joints are employed. Representative of the externally pressurized expansion joints are the X-Press Expansion Joint produced by Pathway Bellows, Inc., of El Cajon, California. These are for use, however, in a straight-line pipeline, not at an angled expansion joint where it is necessary to change the straight-line fluid flow to an angled flow much as does a standard L, T, or Y pipe connection. Providing a externally pressurized expansion joint at such an angled flowpath is one of the objects of this invention.
Another need which has existed in the past has been to produce a bellows-type expansion joint which reduces the massive supporting and anchoring system required for most expansion joints. This problem has been essentially eliminated in straight-line flow by so called pressure-balanced expansion joint. Representative of such straight-line bellows-type expansion joints which are also externally pressurized are (1) the pressure compensated bellows joint disclosed in Soderberg, U.S. Pat. No. 3,241,868 (May 22, 1966) and (2) X-Press II Expansion Joint manufactured by Pathway Bellows, Inc., of El Cajon, California. Both of these pressure compensated, bellows-type expansion joints suffer from several drawbacks, however. For example, they require three bellows, they require many interrelated parts which are expensive and complicated. Further, they require a balancing bellows which must be made with a cross-sectional area which is twice the cross-sectional area of the two on line pipe size bellows in order to achieve the desired pressure-balance inside the joint. This diameter ratio limitation adds to the complicating factors inherent in these pressure-balanced, external-pressure bellows expansion joints. However, their biggest drawback is that they are unsuited for anything but straight line pipe runs at the point where the joint is located and they are not adaptable for location at the point where the pipeline flow must angle away from a straight-line run. The present invention provides a bellows-type expansion joint which is pressure-balanced, is externally pressurized, and can be located at a point in the flow line where the flow line must suddenly deviate from a straight-line flow.
The state of the art at the time the present invention was made for a bellows-type, pressure-balanced expansion joint for an angled flow path was still rather crude. Generally, internal pressurization of the bellows was still employed, heavy outside tie rods were required to balance the pressure of two bellows, and heavy reinforcing was required for the tie rods.